A bodu starting from rest, was onserved to cover ` 20 m ` in ` 1 secnd ` and 1 40 m` during the next second. How far had it travelled before the first observation was taken ?

Explanation

Let the distance travelled in ( t+ 1)th second be ` 20 m` and ( t+ 2)th second be ` 40 m`. Then using
the relation ` D-n = u + a/2 ( 2 n - 10` we gwt
` 20 = 0 + a/2 [ 2 xx ( t+ 1) -1] = a/2 ( 2 r + 3) ` ..(i)
and ` ` 40 =0 + a/2 [ 2 xx ( t + 2) -1] = a/2 ( 2 t + 3) ` ...(ii)
On soving (i) & (ii) we ger , ` a = 20 ms^(-1)`
and ` ` t= 1//2 second`. Distance travelled in (t) seconds
` S = ut + 1/2 at&2 =0 + 1/2 xx 20 xx ( 1/2 )^2 = 2 .5 m` .